Reading signs is the really, really easy part. If your vision system can't read and recognise the signs and signals reliably, it's not even beginning to solve the other problems. Trying to adapt the roads to make this part easier is a terrible return on investment. 99% of what you could do to make roads easier to use for self-driving cars is basic maintenance: making sure the signs, markings, and signals remain clearly visible, which also helps improve the performance of human drivers.